For example, an atomic layer deposition (ALD) apparatus which is a kind of semiconductor deposition apparatus is intended to deposit a film having a thickness of the order of angstroms by alternately introducing component gas and water vapor gas only for a short time each.
For this purpose, in order to make it possible to introduce required flow rates of various gases for depositing a film of, for example, one atomic layer into a deposition chamber, mass flow controllers for controlling the flow rates of the various gases to be introduced into the deposition chamber are driven by pulse control (Patent Literature 1).
Such a mass flow controller driven by the pulse control includes: a resistor arranged in a flow path; a valve arranged on the downstream side of the resistor; and a control mechanism adapted to make the valve alternately repeat an ON interval when the valve is opened and an OFF interval when the valve is closed. More specifically, the mass flow controller flows gas into the internal volume of the flow path between the resistor and the valve to charge it until a predetermined pressure is reached during the OFF interval, and during the ON interval, flows the gas charged in the internal volume to the downstream side.
Further, the valve includes a displacement sensor for measuring the opening level thereof, and the control mechanism is configured to, during the ON interval, perform valve opening level feedback control so that a measured opening level measured by the displacement sensor matches a setting opening level corresponding to the flow rate of the gas to be flowed.
However, as a result of intensive examination by the present inventor, it has been found that in particular, in the case of short pulse width, even when performing the opening level feedback control as described above, the flow rate of the gas actually flowing to the downstream side of the valve have an error with respect to an expected flow rate. That is, it is difficult to achieve flow rate accuracy required for, for example, an atomic layer deposition apparatus only using the simple opening level feedback.